Method and apparatus for removing foreign objects from fluid bed systems

ABSTRACT

A foreign object removal system is disclosed including a removal chamber projecting laterally from the combustion chamber of a fluid bed reactor and connected via a downwardly directed pipe to a material flow control plenum chamber which includes means for fluidizing the mixture of inert fluid bed particles and foreign objects at the bottom of the pipe for lateral movement into an air classifier wherein the foreign objects are dropped to a collection tank and the fluid bed particles are carried upwardly by a stream of classifying air to a deentrainment chamber where their velocity is reduced and they are returned to the combustion chamber.

DESCRIPTION TECHNICAL FIELD

This invention relates in general to fluid bed combustion systems andmore particularly to an improved system for removing foreign objectsfrom the fluid bed.

BACKGROUND ART

Fluid bed reactor systems have been proposed in the past for combustionof various different types of materials. One such fluid bed reactorsystem is described in U.S. Pat. No. 3,589,313. Foreign objects orinerts which are introduced into the system through the material to becombusted collect in the fluid bed. Systems are proposed for removingsuch foreign objects in U.S. Pat. No. 4,196,676 assigned to the assigneeof the present application. The systems disclosed in the latter patentsuffer from a number of disadvantages. The particle flow through theremoval system would plug up. Also fluid bed particles brought back intothe fluid bed would cause mechanical damage and sometimes exit the fluidbed via the opening in the top of the combustion chamber.

DISCLOSURE OF INVENTION

The object of the present invention is to provide an improved method andapparatus for removal of foreign objects from a fluid bed system.

Broadly stated the present invention comprises a foreign object removalchamber projecting laterally outwardly from the combustion chamber, amaterial flow control plenum chamber below the removal chamber, a firstpassageway connecting the removal chamber to a first end of the plenumchamber, and an air classifier and particle return system connecting thesecond end of the plenum chamber first to a collection tank below theplenum chamber for collection of the foreign objects and secondly to thecombustion chamber for return of the inert particles making up the fluidbed. The plenum chamber is provided with means for introducingfluidizing air into the quantity of inert particles and foreign objectsin a direction from the first end to the second end of the chamber.

One of the features and advantages of this invention lies in the factthat the passageway connecting the removal chamber and the plenumchamber serves to seal off the foreign object removal system from thefluid bed system. Another advantage lies in the fact that the fluidizingair introduced into the plenum chamber controls the movement of theinert particles and foreign objects and prevents the foreign objectremoval system from becoming plugged up.

Another feature and advantage of the present invention is the provisionof a de-entrainment chamber means located in the system between the airclassifier and the combustion chamber whereby the inert particles forthe fluid bed are returned to the fluid bed chamber without damage tothe chamber and without the possible loss of the inert particles fromthe chamber.

Additional objects, advantages and features of the present inventionwill become apparent when taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevational sectional view schematicallyillustrating the present invention.

FIG. 2 is an enlarged side elevational view showing a portion of thestructure shown in FIG. 1.

FIG. 3 is an elevational sectional view of a portion of the structureshown in FIG. 2 taken along line 3--3 in the direction of the arrows.

FIG. 4 is a plan view, partly in section, of a portion of the structureshown in FIG. 3 taken along line 4--4 in the direction of the arrows.

FIG. 5 is a perspective view schematically illustrating one of thetuyere for introducing fluidizing air in the foreign object removalsystem.

FIG. 6 is an enlarged elevational sectional view of a portion of thestructure shown in FIG. 5 taken along line 6--6 in the direction of thearrows.

FIG. 7 is an elevational sectional view of a portion of the structureshown in FIG. 3 taken along line 7--7 in the direction of the arrows.

FIG. 8 is an elevational sectional view of a portion of the structureshown in FIG. 2 taken along line 8--8 in the direction of the arrows.

BEST MODE FOR CARRYING OUT THE INVENTION

While it will be appreciated from the following detailed descriptionthat the present invention is applicable to combustion of differenttypes of materials in fluid bed reactors, the invention is ideallysuited to the combustion of low quality fuels which have a largeproportion of foreign material or inert objects. Typical characteristicsof such low quality fuels are high moisture levels such as up to 65% onan as-received basis, high inert levels such as up to 50% on a drybasis, and sizes from fines up to articles 18" in diameter and 6' long.

A system for burning such material is illustrated in FIG. 1 which showsa fluid bed reactor or combustion assembly 11 having an upstandingcombustion chamber 12, typically cylindrical, which is provided in thelower interior portion thereof with a porous particle support structure13 for supporting a bed of granular inert particles 14. A particle bedmaterial for consuming combustible material such as lumber log yarddebris, clarifier sludge, fly ash and char is crystalline beach sand.For cleaner combustible materials such as hog fuel and some coals, arefractory grog can be used. For higher sulfur fuels such as coal andshale, a limestone or dolomite material can be used to react with thesulfur and thereby eliminate emissions of sulfur dioxide. The height ofthe fluid bed can be varied to match combustion requirements ofdifferent fuels.

A first opening or fluidizing air inlet 15 is provided in the combustionchamber 12 below the porous support structure 13 for delivering a streamof air under pressure from the outlet of a fluidizing fan (not shown)via a conveying conduit or pipe 17. A second opening or fuel inlet 18 tothe chamber 12 is provided for introducing combustible material into thecombustion chamber 12 via an elevated feed chute or stack 19 into whichthe combustible material 10 is introduced via a conveyor 20.

Gaseous exhaust products from the combustion which takes place withinthe bed of particles 14 or the region 21 in the combustion chamber abovethe bed of particles 14 are drawn out of the chamber 12 through a thirdopening 22 in the top thereof via a pipe or conduit 23.

The porous support structure 13 for supporting and fluidizing the bed ofparticles 14 is provided with openings 31 which direct the air streaminto the quantity of particles with a velocity vector directed towardone side 32 of the combustion chamber 12 for aiding in the removal offoreign objects 33 such as rocks, oversize inert members, tramp metal,etc. from the combustion chamber via a foreign object removal chamber 34at the one side 32 of the combustion chamber 12.

It will be appreciated that the porous support structure can take one ofa number of different forms. The structure may be a perforateddistribution plate with angle openings or louvers to provide the desiredsideways velocity vector or can consist of a plurality of tuyeresprovided with top perforated members connected either to a duct or amain plenum. A tuyere or bed nozzle 71 is shown by way of example inFIGS. 5 and 6 with a conical chamber 72 provided with a louvered topsurface 73 to provide the desired directional openings 74, and air isfed into the chamber 72 for passage out of the opening 74 from a feedpipe 75 which is connected through a distribution plate which subdividesthe combustion chamber 12.

The apparatus for removing foreign objects from the fluid bed combustionsystem includes a foreign object removal chamber 34 projecting laterallybeyond the sidewall 32 of the combustion chamber 12. Chamber 34 isformed by top and bottom walls 35 and 36, respectively, and threesidewalls 37A, 37B and 37C. Fluidizing means such as tuyeres 39 similarto tuyeres 71 in the fluid bed combustion chamber, are provided forlaterally shifting the mixture of inert bed particles 14 and foreignobjects 33 from a first end of the removal chamber 34 at the sidewall 32of the combustion chamber to a second outboard end at the wall 37B.Fluidizing air is fed to the tuyeres 39 from an air conduit 40A and anair plenum 40B.

A vertically downwardly directed pipe or passageway 38 is provided atthe second or outboard end of the chamber 34 for removing a mixture ofthe inert particles 14 and foreign objects 33 from the removal chamber34. An annular air passage 38A is provided immediately surrounding theupper end of the pipe 38 to keep the top of the pipe clear fromobstruction and plugging.

The lower end of pipe 38 is connected to one or a first end 44A of amaterial flow control plenum 44 formed by top and bottom walls 45 and46, respectively, and a pair of sidewalls 47. The plenum 44 is providedwith means for fluidizing the lower end of the column of mixed inertparticles and foreign objects entering the plenum from the pipe 38. Thefluidizing means includes an apertured angled plate 48 directly at thebottom of pipe 38 and a tuyere 49 covering the remaining bottom surfaceof the chamber 44. Both the plate 48 and the tuyere 49 include surfaceswith angled openings for air from air supply ducts 48A and 49A,respectively, directed so that the air flow is from the first end of thechamber 44 beneath the pipe 38 to a second end of the chamber 44 into anair classifier passage 51.

The air classifier passage includes a vertical pipe 51 extending from aforeign object collection tank 52 located below the plenum chamber 44 toan inert particle deentrainment device 53 located above the plenumchamber 44. The lower end of the pipe 51 projects into a fluid materialsuch as water in the tank 52 or a sealed container for sealing off aircommunications out through the lower end of the pipe 51. A conveyor canbe provided with its initial pickup portion beneath the lower end ofpipe 51 for removal of the foreign objects 33 from the tank 52.

An air stream for the air classifying pipe 51 is introduced via an airsupply pipe 51A into the pipe 51 below the plenum chamber 44. The plenumchamber 44 is a fluidizing conveyor which controls the delivery ofmaterial to the classifying air stream in pipe 51. The upwardly directedair classifying stream in pipe 51 will pick up inert particles from theoutbound end of the plenum chamber 44 and carry them upwardly whilepermitting the heavier foreign objects to drop down in pipe 51 to thetank 52.

The deentrainment device 53 includes structure for reducing the velocityof the inert particles originally from the fluid bed and returning themto the fluid bed. In the preferred embodiment illustrated, thedeentrainment device or chamber 53 includes an enlarged diameter pipesection 54 at the top of the pipe 51 and which opens into an enlargeddiameter angled return pipe 55 leading from the enlarged diameter pipe54 to the chamber 51. By way of illustrative example, for an airclassifier pipe 51 eight inches in diameter and carrying air flow of1050 cubic feet per minute, the deentrainment chamber 53 includes anenlarged diameter pipe 54 approximately four feet long and twelve inchesin diameter and an enlarged diameter angled extension pipe 55approximately two and a half feet long and also twelve inches indiameter.

Insulation is provided at various walls and expansion joints in variouspipes because of the elevated temperature in the combustion chamber andaccess ports are provided at various locations such as an access port34A to the removal chamber 34 and access port 54a to pipe 54 of thedeentrainment device.

FIG. 1 schematically illustrates the air supply connection to variousparts of the system. An air conduit 61 from the pipe 17 passes an airsupply through a control valve 62 to the input tube 40A to the tuyeres39 in the removal chamber 34. A separate air supply from a blower 63provides the air to the control plenum chamber 44 in the air classifiertube 51. This air is conducted via a line 64 and through a valve 65 andbranch line 66 to the input to pipes 48A and 49A for the plenum chamber44. Air from pipe 64 is controlled through valve 67 and connected to theinput pipe 51A to the air classifier pipe.

In the operation of the present invention when the bed of inertparticles 14 has previously been heated, the combustible material 10moves into the bed of particles 14 fluidized by the air stream from thefan 16 whereby the combustible material is heated to ignitiontemperature and combustion takes place. The foreign objects 33 sink tothe bottom of the fluid bed and are conveyed to one side of thecombustion chamber 12 and are removed via the removal chamber 34. Themixture of inert fluid bed particles and foreign objects are movedlaterally of the removal chamber 34 and fill up the pipe 38. In foreignobject removal either intermittently or continuously the fluidizing airintroduced via the openings in plate 48 and tuyere 49 move the mixtureto the opposite end of plenum chamber 44 into the air classifier tube51. The heavier foreign objects drop down the top into the tank 52 whilethe lighter inert fluid bed particles are raised by the classifying airstream to the deentrainment chamber 53 where the particles slow down andare turned into the downwardly angled pipe 55 and are returned to thecombustion chamber.

We claim:
 1. In a fluid bed combustion apparatus having,an upstandingcombustion chamber, a porous support structure within the combustionchamber supporting a quantity of finely divided inert particles, a firstopening into the combustion chamber below the porous structure forintroducing a stream of air for passage up through the porous supportstructure for fluidizing the quantity of particles, a second openinginto said combustion chamber for introducing combustible material whichcontains foreign objects, a third opening at the top of the combustionchamber above the particles for passing products of combustion out ofthe combustion chamber, a foreign object removal opening for removal offoreign objects from the quantity of particles from one side of thecombustion chamber, and means at a plurality of locations beneath thequantity of particles for introducing fluidizing air into the quantityof particles in a lateral direction toward said foreign object removalopening, the improvement comprisinga foreign object removal chamberprojecting laterally outwardly from said combustion chamber, a materialflow control plenum chamber below said removal chamber, and having afirst and a second end, a foreign object collection tank located belowsaid control plenum, a first passageway means connecting said removalchamber to said first end of said plenum chamber for passing inertparticles and foreign objects out of said combustion chamber, particleseparation and return means connecting said second end of said plenumchamber with both said combustion chamber and said collection tank forseparating foreign objects which move to said tank from inert particleswhich move to said combustion chamber, and means at a plurality oflocations in the bottom of said plenum chamber for introducingfluidizing air into a quantity of inert particles and foreign objects ina direction from said first end to said second end of said plenumchamber.
 2. In the apparatus of claim 1 said particle separation andreturn means including an air classifier means for elevating inertparticles above said plenum chamber back into said combustion chamberand dropping foreign objects into said tank.
 3. In the apparatus ofclaim 2 a deentrainment chamber means located above said control plenumfor deentraining inert particles from a classifying stream of air insaid air classifier means and connected to said air classifier means,and a second passageway means connecting said deentrainment chamber withsaid combustion chamber for returning inert particles to said combustionchamber.
 4. In a fluid bed combustion apparatus having,an upstandingcombustion chamber, a porous support structure within the combustionchamber supporting a quantity of finely divided inert particles, a firstopening into the combustion chamber below the porous structure forintroducing a stream of air for passage up through the porous supportstructure for fluidizing the quantity of particles, a second openinginto said combustion chamber for introducing combustible material whichcontains foreign objects, a third opening at the top of the combustionchamber above the particles for passing products of combustion out ofthe combustion chamber, a foreign object removal opening for removal offoreign objects from the quantity of particles from one side of thecombustion chamber, and means at a plurality of locations beneath thequantity of particles for introducing fluidizing air into the quantityof particles in a lateral direction toward said foreign object removalopening, the improvement comprisinga foreign object removal chamberprojecting laterally outwardly from said combustion chamber, a materialflow control plenum chamber below said removal chamber, and having afirst and a second end, a deentrainment chamber means located above saidcontrol plenum for deentraining inert particles from a classifyingstream of air, a foreign object collection tank located below saidcontrol plenum, a first passageway means connecting said removal chamberto said first end of said plenum chamber for passing inert particles andforeign objects out of said combustion chamber, a second passagewaymeans connecting said deentrainment chamber with said combustion chamberfor returning inert particles to said combustion chamber, air classifiermeans connecting said second end of said plenum chamber with both saiddeentrainment chamber and said collection tank for separating foreignobjects which move to said tank from inert particles which move to saiddeentrainment chamber means, and means at a plurality of locations inthe bottom of said plenum chamber for introducing fluidizing air into aquantity of inert particles and foreign objects in a direction from saidfirst end to said second end of said plenum chamber.